Laser radar (lidar) has been used on military and commercial aircraft for the purpose of measuring wind hazards and providing optical air data. Lidar is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The range to an object is determined by measuring the time delay between transmission of a laser pulse and detection of the reflected signal.
Aircraft and wind turbines (or wind turbine generators) operate within complex, on-coming, flow fields and have a distinct need for advanced detection, classification, measurement, warning and/or mitigation of wind hazards. The flow fields may vary from highly laminar through highly turbulent, depending on the local weather, time of day, humidity, temperature, lapse rate, turbine location, local terrain, etc. Wind hazards applicable to wind turbines include gusts, high wind speed, vertical and horizontal wind shear, nocturnal low level jets, convective activity, microbursts, complex terrain-induced flows, Kelvin Helmholtz instabilities, turbulence, and other similar events.
Wind turbines may rotate about either a horizontal or a vertical axis, with horizontal-axis turbines far more common Horizontal-axis wind turbines (HAWT) have a rotor shaft and an electrical generator typically located at the top of a tower, and the rotor shaft is typically parallel with the wind during usage. HAWTs achieve high efficiency since their blades move substantially perpendicular to the wind. Since the tower that supports the turbine produces turbulence behind it, the turbine blades are usually positioned upwind of the tower.
FIG. 1 is a simplified diagram of a horizontal-axis wind turbine 100. The HAWTs may include one, two, three, or more rotating symmetrical blades 102, each having a blade axis approximately perpendicular to the horizontal axis of rotation 104. Turbine blades are generally stiff to prevent the blades from being pushed into the tower by high winds. The blades may be caused to bend by the high winds. High wind speed, gusts and turbulence may lead to fatigue failures of the wind turbines. Blade pitch control is a feature of nearly all large modern horizontal-axis wind turbines to permit adjustment of wind-turbine blade loading, generator shaft rotation speed and the generated power as well as protection from damage during high-wind conditions. While operating, a control system for a wind turbine adjusts the blade pitch by rotating each blade about the blade's axis. Furthermore, wind turbines typically require a yaw control mechanism to turn the axis of wind-turbine rotation, blades and nacelle toward the wind. By minimizing a yaw angle that is the misalignment between wind and turbine pointing direction, the power output is maximized and non-symmetrical loads minimized.